There have been many developments in the field of electromagnetic machines one of which has been to develop an electromagnetic machine typically embodied as a motor which incorporates a circular array of permanent magnets and a similarly arranged plurality of pole pieces around a stator which are energised by a coil so as to produce alternate North and South poles therearound. The rotating field is obtained by commutating the current flowing in the coil so as to obtain interaction between the pole pieces and the permanent magnets. This design allows a very thin motor or other machine to be produced and has the advantage that the power available can be increased by simply mounting additional units on a single drive shaft in the form of a stack.